Jackson County sheriff's candidate Bob Sergi is under criminal investigation for what he says was alleged activity involving his campaign in his bid to unseat his boss, Sheriff Mike Winters.

Oregon Department of Justice spokeswoman Kristina Edmunson confirmed Friday that her agency is in the midst of a criminal investigation of Sergi and that it began at the request of the Jackson County Sheriff's Department. Edmunson declined further comment, including the nature of the allegations.

Sergi was placed on administrative leave Tuesday from his job as a lieutenant and night supervisor at the Jackson County Jail when he was informed of the investigation.

Sergi said a DOJ investigator informed him that the investigation has "something to do with the campaign" but that the investigator did not tell him what specific charge or charges were part of the probe.

"They just said they were investigating me," Sergi said Friday. "That was it."

Sergi said he and his campaign are cooperating with the DOJ but that he has yet to be interviewed for the investigation.

"I'm pretty confident this will be resolved, that I'll be cleared and this will be over," Sergi said. "I didn't do anything."

Sergi, a 57-year-old Central Point-area resident, has worked at the sheriff's department since 2010 after a stint at the Medford Police Department. He was once the jail commander but was most recently a night supervisor when he was placed on leave.

In his campaign for sheriff, Sergi has criticized Winters for spending too much time, money and effort in emergency management rather than in law enforcement.

Winters is running for re-election to the non-partisan post he first won in the 2002 primary. Winters did not return telephone calls seeking comment.

Corey Falls, deputy chief at the Ashland Police Department, is the third candidate in the May 20 primary election.

Oregon Secretary of State records show that Sergi's campaign has raised $8,737 in cash this year, received a $2,500 loan from Sergi and began the year with a carryover balance from last year of $3,788. His campaign has spent $9,846, records show.

Falls' campaign has raised $10,602 in cash this year, received no loans and began the year with a carryover of $9,846. It has spent $15,858 so far, records show.

The Secretary of State's Office shows no contributions or expenditures for Mike Winters' campaign.